1. Field of the Invention
This invention relates generally to preparing thin films for etch patterning. More specifically, the invention relates to preparing thin film substrates and encapsulating material for etch patterning to form the air-bearing surface of a slider.
2. Description of Related Art
Conventional magnetic disk drives are information storage devices that utilize at least one rotatable magnetic media disk with concentric data tracks. They also utilize a read/write transducer for reading and writing data on the various tracks or separate read and write transducers as in the magnetoresistive and giant magnetoresistive heads that have become the trend in the data storage industry as a means of improving data storage density. Disk drives generally also have an air bearing slider for holding the transducer adjacent to the track generally in a flying mode above the media, a suspension for resiliently holding the slider and the transducer over the data tracks, and a positioning actuator connected to the suspension for moving the transducer across the media to the desired data track and maintaining the transducer over the data track during a read or a write operation.
The recording density of a magnetic disk drive is limited by the distance between the transducer and the magnetic media. One goal of air bearing slider design is to “fly” a slider as closely as possible to a magnetic medium while avoiding physical impact with the medium. Smaller spacings, or “fly heights,” are desired so that the transducer can distinguish between the magnetic fields emanating from closely spaced regions on the disk.
In addition to achieving a small average spacing between the disk and the transducer, it is also critical that a slider fly at a relatively constant height. The large variety of conditions that transducers experience during the normal operation of a disk drive can make constancy of fly height anything but a given. If the flying height is not constant, the data transfer between the transducer and the recording medium may be adversely affected.
The manner in which a slider is manufactured and the material the slider is fabricated from can affect fly height. Preferably variations in the physical characteristics of the slider, e.g. due to manufacturing tolerances, should not substantially alter the flying height of the slider. If this result is not achieved, the slider's nominal fly height must be increased to compensate for variations between sliders.
In the past, the processes for defining air bearing surfaces included using a dry-film resist as the etch mask for a single etch step. However, most current air-bearing surface designs use two or more etch steps to provide lower fly heights and better fly height control. Moreover, slider air-bearing designs for lower fly height may incorporate small pads or other features that are difficult to pattern using dry film resists. Liquid resists have much better resolution capability and are preferred for forming the smaller features of the air-bearing design. To process multiple etch designs, an ion milling step and a reactive ion etching step may be used for either of both steps. At certain row spacings the ion milling etch results in redeposited materials being formed on the sides of the rows, which cannot be removed. In addition, the etch profiles obtained after ion milling and reactive ion etching steps have shallow wall profiles which make inspection difficult and affect the flying characteristics of the slider.
U.S. Pat. No. 5,617,273 to Carr, et al. provides the fabrication of a slider in which the head read and write elements protrude out from the air-bearing surface of the slider to allow for closer proximity to the disk. The problem with this design is that the protective carbon overcoat of the slider is removed during the early functioning of the drive, leaving the elements exposed to the drive environment. As a result, corrosion of the elements can occur, which shortens the lifetime of the drive. Corrosion is a leading cause of lower yields for drive components and has become a huge problem as carbon overcoat layers are becoming thinner.
U.S. Pat. No. 5,509,554 to Samuelson, et al. provides the small pads that are necessary for lower fly heights by using imaging methods in which the small pads are attached to larger sacrificial structures. The sacrificial structures must then be removed during the subsequent deep etch step. As a result, all of the areas of the slider that contain the sacrificial structures must be milled to the deepest etch depth. This approach places restrictions on the ABS designers in terms of the placement of deep etch pockets. Many of today's ABS designs could not be fabricated if the methods of this patent were used.
U.S. Pat. No. 5,516,430 to Hussinger provides a planarization procedure that uses alignment fixtures to accommodate liquid resist application. A filled thermoplastic material is then placed on the rows with a substrate on top. The substrate is heated to 400–500° F., causing the encapsulating material (or encapsulant) to melt and flow into the gaps between the rows. The heating process is controlled by maintaining the alignment fixture near ambient temperature to avoid the encapsulant from sticking to the fixture. Sufficient heat is applied to melt the material near the air-bearing surface (ABS) that may contain thermally sensitive transducers.
A disadvantage of using the Hussinger process is the potential for seepage of material onto the air-bearing surface of the slider. The presence of tapers at the leading edge of the slider provides a conduit by which the material can reach the ABS. Contamination of the ABS also causes photoresist imaging and adhesion problems.
Another problem with the Hussinger procedure is the need for pins to isolate the rows and provide constant gaps between rows. Once the planarization method is carried out, the pins are removed, causing holes to exist in the encapsulated carrier. These holes or defects will then affect the uniformity of the resist coating. In the areas of the carrier close to the void and extending in a radial direction outward from the void, there will be severe effects on resist thickness. After patterning and etch, the resist thickness variation will be translated into the ABS pattern in the form of etch profile variation, which will cause differences in fly height. Large differences in fly height are unacceptable because of the effect on head performance; thus, these heads will be discarded, lowering yield. The holes will also contribute to yield loss since sliders near holes will be subjected to redeposition during etch steps. Furthermore, the high temperature requirement for this procedure (400–500° F.) may preclude use of certain thermally sensitive transducers such as giant magnetoresistive sensors, which are used to produce higher density magnetic storage products.
In response to these disadvantages, U.S. Pat. No. 5,932,113 to Kurdi, et al. (hereinafter referred to as the “Kurdi patent”) provides a process for preparing an air-bearing slider that uses an adhesive film made by Nikko Dento and an acrylic encapsulating fluid to fill the recesses between the rows during etching. The Kurdi method attempts to eliminate redeposition contamination during etching and to protect the active transducer devices from handling damage. According to the Kurdi patent, thin films to be etched are applied to a carrier, each of the thin films separated by a recess. Each of the thin films may comprise a transducer-laden air-bearing surface (ABS). An adhesive film is then generally applied to the ABS side of the thin films. A fluid is then deposited in the recess, which is held in the recess by the adhesive film. The fluid may then be cured and the adhesive film removed to provide a planar surface. The ABS side of the row may then be coated with an etch mask, the etch mask developed and air bearing surface patterned.
The Kurdi patent discloses the use of Nitto Denko dicing tape and an acrylic encapsulation fluid to partially fill the gaps between rows. However, implementation of the Kurdi patent may give rise to step heights in the planar surface, resulting in large variations in the liquid resist coating thickness, which are problematic for the air-bearing surface patterning process. It could produce indentations of about 30 microns from the air-bearing surface in the gaps that separate rows. Several factors contribute to the formation of such indentations. First, it is the flexibility of the tape that causes the tape to sink due partly to its own weight and lack of stiffness. Second, the shrinkage of the encapsulant also contributes to the increase in the depth of the indentations. These indentations result in step heights of about 30 microns from the air-bearing surface. The relatively large step heights created by the Kurdi process would affect uniformity of the thickness of the resist coating during the etching process.
It is therefore desirable to create methods that provide thin films with improved planarization, and that overcomes the drawbacks in the prior art.